Decline of Colorado River Is Severe

Dec. 6

By Lee Dye

The Colorado River, which gushed across the land with such gusto that it carved the majestic Grand Canyon in a measly five million years, once reigned as an unchallenged force in shaping and nurturing the Southwest.

But then humans came along, and the mighty river has been reduced to a trickle in some places, even dying out in the desert during dry years before it reaches the Gulf of California.

It doesn’t take a lot of smarts to figure out that if you take away the water, creatures and plants that depend on it will die. But now scientists have compiled an extensive record of what the Colorado was like before humans re-engineered the river, compared to what it’s like now. It’s not a pretty picture.

Dried Up and Lifeless

About 95 percent of the marine life in the river’s delta has been wiped out in less than 70 years. Where great beds of clams once flourished, ultimately providing the white sand that nature reshaped into large offshore islands, very little survives today. What’s astonishing is the scale of the impact.

“It’s pretty shocking,” says paleontologist Michal Kowalewski of Virginia Tech, one of the leaders in a four-university study of the price the environment has paid for reshaping the river. The study was published in last week’s issue of the journal Geology.

Today, the river is, at best, a stream when it reaches the gulf that separates the Baja peninsula and mainland Mexico. The region used to be one of the most biologically productive areas on the planet, supporting billions of clams and other marine life in the nutrient-rich waters of the delta.

Measuring by Clams

The researchers concentrated on clams, because their hard shells have survived the ravages of time, and those shells provide a biological yardstick of the marine ecosystem, according to paleontologist Karl W. Flessa of the University of Arizona, one of the principal investigators.

“The clams were in a sense a proxy for the whole marine ecosystem,” Flessa says. “There were so many there because of the very high productivity of marine microorganisms” which thrived in the nutrient-rich waters. Thus more clams means more wildlife ranging from tiny sea creatures to fish to birds.

The researchers found that clams were so abundant that a total of more than two trillion thrived in the delta over the last 1,000 years, a density of about 50 clams per square meter at any time.

That number today has been reduced to about three clams per square meter, if they can be found at all.

Thus the scientists estimate a drop in marine life of at least 20 fold, but Kowalewski says that figure is “quite conservative.”

”I think 20 times is a pretty staggering number, but in fact my hunch is that it’s probably much more than that,” he says. There may have been 100, or even 200 times more marine life in the delta before the 1930s ushered in a new life for the Colorado, he adds.

Distributing its Flow

Some would argue, of course, that what humans took away, humans put to good use. Electricity from the Hoover Dam brought jobs and power to areas like Las Vegas, allowing that region to become one of the fastest growing metropolitan areas in the country. Without the dam, the lights of ”glitter gulch” would be more like candles.

Water was diverted from the river to farms and cities, turning some desert regions into bread baskets, and allowing major urban centers like Phoenix and the megalopolis of Southern California to prosper.